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Re: Graflarger Repair

Originally Posted by AuditorOne

I opened up the light box and that part looks good. The cold light grid looks ok but until I can get power to it I won't be certain. (No scorched wires or black marks. ) I didn't really expect that the power made it all the way through to this point since the switch was in the off position when I plugged it in but you never know.

Next I will pop the transformer box and see if I can start tracing continuity through the power wires. I do hope that the transformer didn't fry.

I do own a few electrical gadgets and tools including a volt/ohm meter. Nothing as nice as my son's Fluke but they will do for this device. If it does get to complicated I'll send it to him for a look.

I did a short stint as an apprentice to a TV repairman one or two years ago but I was too slow to make a living at it so I went on to other more lucrative pursuits.

I take it from everyone's responses that there are no qualified repair shops that handle this equipment any longer.

No regular shops left, but these are not rocket science either (if you have some more than basic electrical background)...

The main issue with mine was power cord insulation that had turned to dust, so a no brainer... I was concerned about the transformer to head cord, but it seemed to be made of different materials/dielectric than the AC cord (as I opened the head, looked at the insulation on that end of the cord, and saw it was still supple and intact so I tested/continued)... If that cord was bad, it would have been real trouble as the wires headed straight down into the tar potting material inside the housing, but after doing short tests (and measuring the resistance of the transformer secondary and primary) it seemed OK... With a new AC cord + fuse installed, then powered it up on the bench and measured about 570VAC (I think I remember it being something like that)... So that's a start...

On the grid end there was much corrosion under the wire nuts connecting the HV cord to the thin grid wire ends, so I cleaned them up (be very careful as these lead wires are thin and maybe brittle, and don't allow the heavy cable to stress these while installing and secure well), tested them together and there was light!!! Then it was off to restore the rest of the head...

If you have trouble getting the transformer housing open (stuck like a giant clam), turn it upside down and hit it with a heat gun for a minute or two, to heat the tar (that may have dripped a little into the cover seams) and pry the corners each a little at a time until it pops off...

The temp regulation I upgraded to was a big help getting consistent exposures from these, because before, even with a shuttered lens and leaving it on throughout the printing session, exposures would bounce around quite a bit, so it was a big help...

Re: Graflarger Repair

I have A LOT of experience working on vintage electronics, many units considerably older than this.

- Leigh

Yea, Leigh's great and VERY knowledgeable, fantastic posts on Antique Radio Forums, TekScopes, etc... If you can't figure it out, take him up on his offer!!!!

But Leigh, for right now testing, I don't remember transformer turns ratios formulas, but about what would be the resistance for the primary and secondary of this transformer... I know it converts 110VAC to about 570VAC (unloaded), so this would be a useful (safe) test for him to try (with an ohmmeter)...

(note/ Leigh, if I see kites flying from your castle some stormy night, I'll keep the (angry) villagers away...) :-)

Re: Graflarger Repair

Originally Posted by LabRat

But Leigh, for right now testing, I don't remember transformer turns ratios formulas, but about what would be the resistance for the primary and secondary of this transformer... I know it converts 110VAC to about 570VAC (unloaded), so this would be a useful (safe) test for him to try (with an ohmmeter)...

(note/ Leigh, if I see kites flying from your castle some stormy night, I'll keep the (angry) villagers away...) :-)

Hi Steve,

Thanks for the kind words.

Unfortunately, you cannot predict winding resistance for any transformer. It's a function of the current-carrying capacity of the particular winding and of the over-all transformer design.